A high-temperature mechanical seal can reduce the need for external cooling in some ANSI process-pump services, but removing a cooling plan is not automatic. The decision depends on seal-face temperature, vapor-pressure margin, fluid cleanliness, thermal cycling, materials and the required containment level. Configure the pump and seal as one engineered package, then verify fitment and operating limits before ordering.
What Is API Plan 23?
API Plan 23 is a closed-loop circulation circuit for a single mechanical seal. Process liquid circulates from the seal chamber through a heat exchanger and returns to the seal chamber, reducing the temperature around the seal faces without continuously sending hot process liquid to an external utility system. It is commonly considered for suitable hot services, but the circulation path, cooler duty, seal design and process cleanliness must be confirmed for the application.
API Plan 23 is not a universal substitute for every seal-cooling arrangement. If the process can foul the circuit, the heat load is too high, circulation is unreliable, or the seal supplier’s pressure and temperature limits are exceeded, another plan or containment strategy may be required. See the API Plan 23 reference for the basic circuit concept.
Why high temperature creates seal problems
At elevated temperature, the liquid film between mechanical-seal faces becomes harder to maintain. Flashing, coking, thermal expansion and secondary-seal degradation can all increase leakage or wear. The bulk-fluid temperature is only one input: pressure in the seal chamber, shaft speed, flush or barrier-fluid conditions, solids, startup procedure and the pump’s heat path also matter.
For ANSI process pumps, the seal chamber, shaft sleeve, impeller, casing and power end must be checked together. A seal that fits dimensionally may still be unsuitable hydraulically, mechanically or operationally. ANSI B73.1 dimensional compliance does not by itself prove that every internal part or every hydraulic curve is interchangeable.
API Plan 23 vs High-Temperature Seal Without External Cooling
| Decision area | API Plan 23 | High-temperature seal without external cooling |
|---|---|---|
| Auxiliary equipment | Requires a circulation circuit, heat exchanger and associated piping, supports and inspection. | Can reduce auxiliary equipment, but the seal chamber still needs a suitable heat path and operating control. |
| Seal-face temperature control | Closed-loop circulation removes heat from the seal-chamber fluid when the circuit is correctly sized and operating. | Relies more on seal design, chamber geometry, process conditions and pump heat dissipation. |
| Process-fluid conditions | Requires a circulation path that can tolerate the process fluid and expected fouling or solids. | May suit cleaner services, but chemistry and solids still govern face, elastomer and metal selection. |
| Vapor-pressure margin | Must be checked at the seal-chamber pressure and the temperature reached in the circuit. | Must be checked directly at the seal faces; loss of margin can cause flashing and unstable lubrication. |
| Maintenance | Adds cooler, piping and instrumentation inspection to the seal-maintenance plan. | May simplify the auxiliary system but can make seal selection and thermal control more critical. |
| Limits | Depends on circulation, exchanger duty, seal design and supplier-specific pressure/temperature limits. | Depends on the selected seal, chamber, fluid, speed, pressure and supplier-specific operating envelope. |
API Plan 53 is different: it is a pressurized barrier-fluid system normally associated with dual seals. It may support a containment strategy, but it is not an interchangeable cooling plan or an equivalent purpose to API Plan 23.
Seal technologies used in hot service
| Approach | Where it can fit | Main benefit | Important check |
|---|---|---|---|
| Conventional seal with cooled flush | Services where cooling is available and acceptable | Established design with controlled seal-face environment | Cooling-water quality, exchanger duty, piping-plan reliability and reheating impact |
| High-temperature cartridge seal with FFKM | Moderate-to-high temperature services within the seal maker’s rating | Can simplify the auxiliary system | Actual temperature, chemical compatibility and thermal-cycling life of the elastomer |
| Stationary metal-bellows seal | Hot services where dynamic secondary seals are a concern | Reduces dependence on a dynamic elastomer | Bellows fatigue, pressure, speed, solids and face-material compatibility |
| Dual pressurized seal | High containment or difficult process fluids | Barrier fluid protects the faces and limits process leakage | Barrier-fluid system, pressure control, instrumentation and maintenance plan |
| Gas-lubricated seal | Specialist applications with suitable clean, dry gas | Very low process contact at the seal faces | Gas quality, supply reliability, pressure control, speed and supplier-specific limits |
Temperature limits in this table are intentionally qualitative. Do not select a seal from a generic temperature number: the seal manufacturer’s rating, materials and operating envelope must be checked against the complete application.
Four checks before reducing or removing seal cooling
1. Temperature and vapor-pressure margin
Confirm maximum continuous and upset temperatures at the seal faces, not only the nominal process temperature. Compare the seal-chamber pressure with the fluid vapor pressure at the relevant face temperature. If the margin is inadequate, a higher-pressure barrier system or another containment strategy may be required.
2. Fluid chemistry and solids
Review concentration, pH, chlorides, contaminants, solids, velocity and oxidizing or reducing conditions. These factors influence face materials, elastomers, metal parts and wet-end metallurgy. Alloy 20 (UNS N08020) and CN7M are not the same specification; C-276 (UNS N10276) and CW2M are not interchangeable descriptions. Material selection should follow the actual fluid and project documentation.
For corrosive hot service, consider the casing, impeller, shaft sleeve and seal hardware together. Obtain material certificates and, when required, PMI or other verification rather than relying on a material name alone.
3. Thermal cycling and startup
Frequent starts and stops can be more damaging than steady operation. Define the warm-up sequence, allowable ramp rate, minimum flow and shutdown procedure. Preheating may be appropriate, but the method must be compatible with the casing, process and site safety requirements.
4. Fitment and duty-point confirmation
For a replacement pump or part, verify model, size, group, frame, shaft arrangement, seal chamber, shaft sleeve, impeller trim, material and duty point. Request approved drawings, dimensional inspection records, heat-number traceability and hydrostatic-test documentation where applicable. A cross-reference is an engineering starting point, not a blanket promise of universal compatibility.
For related fitment work, see the OEM part-number cross-reference, the ANSI pump mechanical seals and seal chambers guide, the Durco Mark III 2 compatible-parts guide and the Goulds 3196 versus Durco Mark III comparison.
Cooling-system economics: what to measure
Removing a cooler can reduce equipment count, piping, controls and maintenance, but the business case should use measured or quoted project data. Record cooling-water flow, temperature rise, pump power, exchanger duty, process-fluid reheating duty, maintenance hours and the cost of an unplanned seal change. Avoid assuming a universal energy saving: the result varies with fluid properties, operating hours, utility prices and the selected seal plan.
Inspection and documentation checklist
- Approved pump and seal drawings, including seal-chamber and shaft-sleeve dimensions.
- Duty point, maximum temperature, pressure, speed, solids and thermal-cycle profile.
- Seal-face, elastomer, bellows and barrier-fluid compatibility confirmation.
- Material certificates with heat-number traceability; PMI when specified by the project.
- Dimensional inspection, runout or concentricity records and hydrostatic testing where required.
- Startup, warm-up, flush or barrier-system instructions and spare-parts identification.
Request a technical fitment review
Send the current pump model, size, fluid, temperature, pressure, speed, solids, seal arrangement and duty point. ANSI Pumps Pro can review the replacement scope and identify which dimensions, materials and operating limits require confirmation.
Frequently Asked Questions
Can a high-temperature seal always eliminate a cooling system?
No. It may be suitable when the seal-face temperature, vapor-pressure margin, chemistry, solids and thermal cycling are within the selected seal’s documented limits. A dual seal, barrier system or cooled arrangement may still be the safer choice.
Does ANSI B73.1 prove that a replacement seal or pump part will fit?
No. The standard helps define pump dimensions, but the specific model, group, frame, seal chamber, shaft sleeve, materials, impeller trim and duty point must still be checked.
What information is needed for a high-temperature seal review?
Provide the pump model and size, fluid and concentration, normal and maximum temperature, suction and discharge pressure, speed, solids, operating hours, starts per day, current seal plan and any available drawings or inspection records.
Technical source
For the API Plan 23 circuit description, consult the John Crane API Plan 23 reference. Application limits must still be confirmed with the seal supplier and project documentation.
